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United States Patent |
5,318,635
|
Kasica
,   et al.
|
June 7, 1994
|
Continuous coupled jet-cooking/spray-drying process and novel
pregelatinized high amylose starches prepared thereby
Abstract
A continuous coupled jet-cooking/spray-drying process for processing
inherently water-dispersible or water-soluble crystalline polymers, such
as starches, polygalactomannan gums, and fully hydrolyzed polyvinyl
alcohols, is disclosed. It involves the steps of: (a) forming a slurry or
paste of the polymer and water, (b) jet-cooking the slurry or paste with
steam at a temperature sufficient to fully disperse or solubilize the
polymer, (c) immediately conveying and introducing under elevated
temperature and pressure the jet-cooked dispersion or solution into a
nozzle of a spray-dryer chamber, (d) atomizing the jet-cooked dispersion
or solution through the nozzle, (e) drying the atomized mist within the
spray-dryer chamber at a temperature sufficient to dry the polymer; and
(f) recovering the dried polymer as a water-dispersible or water-soluble
powder. High amylose starches (above about 40% amylose) prepared by this
process are characterized in that the starch is substantially
non-crystalline and substantially non-degraded. Starch mixtures, mixtures
of high amylose starches and other starches, gums, or polyvinyl alcohols
can be co-processed.
Inventors:
|
Kasica; James J. (Somerville, NJ);
Eden; James L. (East Millstone, NJ)
|
Assignee:
|
National Starch and Chemical Investment Holding Corporation (Wilmington, DE)
|
Appl. No.:
|
919673 |
Filed:
|
July 27, 1992 |
Current U.S. Class: |
127/69; 127/28; 127/32; 127/65; 127/67; 426/661; 536/102 |
Intern'l Class: |
C08B 030/00; C08F 016/06; C08F 008/00 |
Field of Search: |
127/28,32,65,67,69
426/661
536/102
|
References Cited
U.S. Patent Documents
H561 | Dec., 1988 | Brown et al. | 426/568.
|
1516512 | Nov., 1924 | Stutzke.
| |
1901109 | Mar., 1933 | Maier.
| |
2314459 | Mar., 1943 | Salzburg | 99/139.
|
2582198 | Jan., 1952 | Etheridge | 127/28.
|
2805966 | Sep., 1957 | Etheridge | 127/32.
|
2919214 | Dec., 1959 | Etheridge | 127/28.
|
2940876 | Jun., 1960 | Elsas | 127/28.
|
3086890 | Apr., 1963 | Sarko et al. | 127/69.
|
3133836 | May., 1964 | Winfrey et al. | 127/71.
|
3137592 | Jun., 1964 | Protzman et al. | 127/32.
|
3234046 | Feb., 1966 | Etheridge | 127/28.
|
3321359 | May., 1967 | Shaughnessy | 127/28.
|
3332785 | Jul., 1967 | Jycgubie et al. | 99/139.
|
3391003 | Jul., 1968 | Armstrong et al. | 127/32.
|
3424613 | Jan., 1969 | Huber et al. | 127/32.
|
3443990 | May., 1969 | Decnop | 536/102.
|
3515591 | Jun., 1970 | Feldman et al. | 127/69.
|
3553196 | Jan., 1971 | Mark et al. | 127/32.
|
3607394 | Sep., 1971 | Germino et al. | 127/69.
|
3630775 | Dec., 1971 | Winker | 127/71.
|
3637656 | Jan., 1972 | Germino et al. | 260/233.
|
3928055 | Dec., 1975 | Brailsford et al. | 106/214.
|
4256771 | Mar., 1981 | Henderson et al. | 127/32.
|
4280851 | Jul., 1981 | Pitchon et al. | 127/28.
|
4579944 | Apr., 1986 | Harvey et al. | 536/102.
|
4721655 | Jan., 1988 | Trzasko et al. | 162/178.
|
4859248 | Aug., 1989 | Thaler et al. | 127/32.
|
4871398 | Oct., 1989 | Katcher et al. | 127/69.
|
5051271 | Sep., 1991 | Iyengar et al. | 426/661.
|
5131953 | Jul., 1992 | Kasica et al. | 127/65.
|
5188674 | Feb., 1993 | Kasica et al. | 127/69.
|
Primary Examiner: Breneman; R. Bruce
Assistant Examiner: Hailey; P. L.
Attorney, Agent or Firm: Kelley; Margaret B.
Parent Case Text
This application is a division of application Ser. No. 697,659, filed May
8, 1991, now U.S. Pat. No. 5,188,674 which is a division of Ser. No.
242,657 filed Sep. 12, 1988, now U.S. Pat. No. 5,131,953.
Claims
What is claimed is:
1. A pregelatinized, spray-dried, non-granular starch powder of a modified
starch base having an amylose content of above about 40%, pregelatinized
by a coupled, continuous jet-cooking/spray-drying process, and
characterized in that the starch is substantially non-crystalline and
substantially non-retrograded and has a bulk density higher than the bulk
density of the same base starch pregelatinized by jet-cooking and
spray-drying in two separate steps.
2. A pregelatinized, spray-dried, non-granular starch powder of a modified
starch base containing amylose in an amount of up to about 40%,
pregelatinized by a coupled, continuous jet-cooking/spray-drying process,
and characterized in that the starch is substantially non-crystalline and
has a bulk density higher than the bulk density of the same base starch
pregelatinized by jet-cooking and spray-drying in two separate steps.
3. A pregelatinized, spray-dried, non-granular starch powder which
comprises a mixture of a pregelatinized, spray-dried, non-granular starch
powder of a modified starch base having an amylose content of above about
40% and a pregelatinized, non-granular, spray-dried starch powder of a
modified starch base containing amylose in an amount of up to about 40%,
the starch powders pregelatinized by a continuous coupled
jet-cooking/spray-drying process, and characterized in that the starch
powders are substantially non-crystalline and have bulk densities higher
than the bulk densities of the same base starches pregelatinized by
jet-cooking and spray-drying in two separate steps, and further
characterized in that the modified starch base having the amylose content
of above about 40% is substantially non-retrograded.
4. A mixture of (a) a pregelatinized, spray-dried, non-granular starch
powder pregelatinized by a continuous coupled jet-cooking/spray-drying
process and (b) a fully pre-dispersed, jet-cooked/spray-dried gum;
characterized in that the pregelatinized starch powder is substantially
non-crystalline, has a bulk density higher than the bulk density of the
same starch pregelatinized by jet-cooking and spry-drying in two separate
steps, and is substantially non-retrograded when the starch has an amylose
content of above about 40%; and characterized in that the pre-dispersed
gum is cold-water-dispersible.
5. A fully pre-dispersed, jet-cooked/spray-dried locust bean gum which is
cold-water-dispersible.
6. A fully pre-dispersed, jet-cooked/spray-dried, substantially fully
hydrolyzed polyvinyl alcohol which is cold-water-dispersible.
Description
BACKGROUND OF THE INVENTION
This invention relates to a process for jet-cooking and spray-drying
water-dispersible or water-soluble polymers, especially high viscosity
starches such as high amylose starches. It also relates to the unique
pregelatinized high amylose starches produced thereby.
Pregelatinized starches (i.e., cold-water-dispersible starches) are
typically prepared by thermal, chemical, or mechanical gelatinization. The
term "gelatinized" or "cooked" starch refers to swollen starch granules
which have lost their polarization crosses and which may or may not have
lost their granular structure.
The thermal processes generally used to prepare such starches include batch
cooking, autoclaving, and continuous cooking processes in a heat exchanger
or jet-cooker. The thermal dispersion of a granular starch in water
involves a complex mechanism. See the discussion at pp. 427-444 in Chapter
12, by Kruger & Murray of Rheology & Texture in Food Quality, Edited by T.
M. DeMan, P. W. Voisey, V. F. Rasper, and D. W. Stanley (AVI Publishing,
Westport, Conn. 1976), at pp. 449-520 in Chapter 21 of Starch: Chemistry &
Technology, Vol. 2, edited by R. L. Whistler (Academic Press, New York,
N.Y. 1967) and at pp. 165-171 in Chapter 4 by E. M. Osman of Food Theory
and Applications, edited by P. C. Paul and H. H. Palmer (John Wiley &
Sons, Inc., New York, N.Y. 1972). The process begins at the gelatinization
temperature, as water is absorbed into the starch granules, and continues
as the hydrated granules swell and disrupt into smaller granule fragments
until the starch finally approaches a molecular dispersion. The viscosity
of the cook changes significantly during this process, increasing as the
granules hydrate and swell and decreasing as the granular fragments are
reduced in size. An appropriate amount of shear aids in breaking down the
swollen granular fragments to give a molecular dispersion without
substantial molecular degradation.
Pregelatinized starches are typically prepared by spray-drying,
drum-drying, or extrusion.
Drum-drying involves simultaneously cooking and drying a starch slurry or
paste on heated, rotating drums. Cooking and drying are accomplished over
a period of time as determined by the temperature and rotation rate of the
drums. The dried sheets are scraped off the drum with a metal knife and
then ground. This process can be conveniently carried out at high solids
content (typically about 43% maximum). The disadvantage of drum-drying is
that this method generally only partially disperses the starch (i.e., the
starch is not completely gelatinized) and this can result in poorly
dispersible powders having undesirable textures when redispersed.
Extrusion may also be used to simultaneously cook and dry starches (see
U.S. Pat. No. 3,137,592 issued Jun. 16, 1964 to T. F. Protzman et al.).
This method involves the physical working of a starch-water mixture at
elevated temperature and pressure, causing the gelatinization of the
starch, followed by expansion during flashing off the water after exiting
from the extruder. The temperature and pressure are generated by
mechanical shear between the rotating screw (auger) and cylindrical
housing (barrel) of the extruder. Cooking is accomplished with both
thermal and mechanical energy as the starch is forced through the system.
This typically results in high viscosity during processing due to
incomplete cooking and the final products are typically degraded due to
molecular breakdown caused by excessive shear. Upon redispersion, the
powders can give undesirable grainy textures, especially when low moisture
starches are processed, due to incomplete dispersion during cooking. When
starch is processed in the presence of additional water, a further drying
step is required after the extrudate exits the extruder. This extended
drying time further exaggerates the undesirable textures upon
redispersion.
The following patents describe various processes for preparing
pregelatinized starches.
U.S. Pat. No. 1,516,512 (issued Nov. 25, 1924 to R. W. G. Stutzke)
describes a process for modifying starch in which starch slurries are
forced through a heated pipe coil and then through a spraying orifice into
a drying chamber. The slurries are processed with or without acid. The
slurries are forced through the coil at excessively high pressures (e.g.,
1000 lbs.) in order to insure against the possibility of vaporizing the
liquid under treatment. Steam is maintained at 35-110 pounds of pressure.
The temperature of the air introduced into the drying chamber is about
121.degree. C. (250.degree. F.), which is reduced to about 96.degree. C.
(204.degree. F.) at the point of evaporation. The resulting starches are
hydrolyzed and are about 15-75% soluble in cold water.
U.S Pat. No. 1,901,109 (issued Mar. 14, 1933 to W. Maier) describes a
spray-drying process in which starch slurries are atomized into a stream
of heated air containing water vapor in such amount that vaporization of
the water from the atomized particles occurs at a temperature above the
gelatinization temperature of the starch and below the temperature at
which further alteration (e.g., hydrolysis) occurs The process can be
carried out with or without a chemical gelatinization agent.
U.S. Pat. No. 3,630,775 (issued Dec. 28, 1971 to A. A. Winkler) describes a
spray-drying process in which a starch slurry is maintained under pressure
during heating and continued under pressure through the atomization step.
The pressure is interdependent with viscosity, temperature, and apparatus.
The pressure requirement is that necessary for atomization and is in
excess of that necessary to prevent vaporization of water in a slurry of
high solids at elevated temperatures. The heating time is that which is
sufficient to allow substantially complete gelatinization and
solubilization of the starch if previously ungelatinized. Typically, the
slurries (10-40% solids) are preheated to 54.degree.-171.degree. C.
(130.degree.-340.degree. F.), pumped under 2,000-6,800 psi of pressure
through a continuous tubular heat exchanger, and heated to
182.degree.-304.degree. C. (360.degree.-580.degree. F.)(which result in
starch temperatures of 163.degree.-232.degree. C.-325.degree.-450.degree.
F.). Retention time of the starch in the cooker is 1.0-2.5 minutes. A
conventional spray-dryer with a pressure type atomizing nozzle is used.
The resulting starches are characterized as having less than 12% moisture,
greater than 33 lb/ft.sup.3 bulk density, and greater than 50% cold-water
solubility.
U.S. Pat. No. 4,280,851 (issued Jul. 28, 1981 to E. Pitchon et al.)
describes a spray-drying process for preparing granular pregelatinized
starches. In this process a mixture of the granular starch in an aqueous
solvent is cooked or gelatinized in an atomized state. The starch which is
to be cooked is injected through an atomization aperture in a nozzle
assembly to form a relatively finely-divided spray. A heating medium is
also injected through an aperture in the nozzle assembly into the spray of
atomized material so as to heat the starch to the temperature necessary to
gelatinize the starch. An enclosed chamber surrounds the atomization and
heating medium injection apertures and defines a vent aperture positioned
to enable the heated spray of starch to exit the chamber. The arrangement
is such that the lapsed time between passage of the spray of starch
through the chamber, i.e., from the atomization aperture and through the
vent aperture, defines the gelatinization time of the starch. The
resulting spray-dried, pregelatinized starch comprises uniformly
gelatinized starch granules in the form of indented spheres, with a
majority of the granules being whole and unbroken and swelling upon
rehydration. Nozzles suitable for use in the preparation of these starches
are also described in U.S. Pat. No. 4,610,760 (issued Sep. 9, 1986 to P.
A. Kirkpatrick et al.)
U.S. Pat. No. 3,086,890 (issued Apr. 23, 1963 to A. Sarko et al.) describes
a process for preparing a pregelatinized isolated amylose powder. It
involves autoclaving a slurry of an isolated amylose having an intrinsic
viscosity of 1.3-2.9 at 191.degree. C. (375.degree. F.) under 5-140 psig
of pressure for 1-60 minutes at 0.1-25% solids, cooling the dispersion to
90.degree. C. (194.degree. F.) , and drum-drying on a
110.degree.-200.degree. C. (230.degree.-392.degree. F.) surface. The
retention time on the drum is 40-75 seconds using a nip gap of 0.001 inch
or less. The resulting powders have amorphous X-ray diffraction patterns,
intrinsic viscosities of 1.3-2.9, and form irreversible gels when
redispersed.
Pregelatinized starches may be made by a two step spray-drying process
which is in current industrial use. Modifications of this conventional
process are described in U.S. Pat. No. 2,314,459 (issued Mar. 23, 1943 to
A. A. Salzburg) and U.S. Pat. No. 3,332,785 (issued Jul. 25, 1967 to E.
Kurchinke). In the typical process an aqueous starch slurry is cooked,
usually by atmospheric vat cooking or by cooking in a heat exchanger or by
steam injection jet-cooking, held at atmospheric pressure in a tank (often
a cooking tank in batch processes or a receiver tank for pressurized
cooking processes), and subsequently spray-dried. The post-cooking holding
period allows the batchwise addition of additives, temperature regulation,
and/or cooking at rates which do not match the spray-dryer capacity. On
exiting the holding tanks the temperature of the feed to the spray-dryer
may range from 38.degree.-93.degree. C. (100.degree.-200.degree. F.).
Atomization is effected by a single fluid pressure nozzle, a centrifugal
device, or a pneumatic nozzle. This process is usually limited to
"thin-cooking starches", i.e., converted starches where the polymeric
structure has been degraded by acid hydrolysis, enzymatic degradation,
oxidation and/or high levels of mechanical shear. Converted starches can
be used at higher solids because their pastes are lower in viscosity and
can be atomized. The cooks of unmodified starches are difficult to atomize
because of their high viscosity and therefore, if spray-dried, are
processed at low solids. Another limiting factor of conventional processes
is that, at temperatures achieved at atmospheric pressure, many polymers
associate and/or retrograde causing an increase in viscosity. See U.S.
Pat. No. 3,607,394 discussed below.
U.S. Pat. No. 3,607,394 (issued Sep. 21, 1971 to F. J. Germino et al.) is
directed to a process for preparing a pregelatinized, cold water
dispersible starch from a granular starch which contains at least 50%
amylopectin (i.e., not more than 50% amylose). Suitable starches include
cereal starches such as corn, wheat and barley, tuber starches such as
potato and tapioca, and waxy starches such as waxy maize, waxy rice, and
waxy sorghum. The high amylose starches, those which contain 60% or more
amylose, as well as isolated amylose itself, are not suitable because
their gelling characteristics are undesirable for the applications
contemplated (i.e., where smooth pastes having a low initial viscosity and
minimal setback). The process involves pasting at at least 149.degree. C.
(300.degree. F.), with the upper limit being that at which substantial
molecular degradation of the starch occurs, e.g., over about 232.degree.
C. (450.degree. F.). The starch paste is then dried very rapidly in any
suitable apparatus, e.g., a drum-dryer, spray-dryer, belt dryer, foam mat
dryer or the like. The only requirement is that the apparatus be capable
of drying the starch paste very rapidly to prevent retrogradation or
aggregation prior to removal of the water. Also it is preferred that the
paste be fed to the dryer very quickly because the longer it is held at a
high temperature the greater is the likelihood of degradation.
Structurally the products are characterized by complete granular
fragmentation.
It is well known that high amylose starches are especially difficult to
disperse and require higher temperatures and higher shear levels than low
amylose starches such as corn, potato, wheat, rice, tapioca, and the like.
Autoclaving or indirect heating, such as in a heat exchanger, are cooking
processes that tend to produce dispersions that are complex colloidal
mixtures, especially with the difficult to disperse high amylose starches.
The mixtures consist of intact granules, residual granular fragments and
dissolved polymer. Jet-cooking provides appropriate shear levels and more
readily gives a dispersion approaching complete solubility at a molecular
level (see U.S. Pat. Nos. 2,805,966 (issued Sep. 10, 1957 to O. R.
Ethridge); 2,582,198 (issued Jan. 8, 1957 to O. R. Ethridge); 2,919,214
(issued Dec. 29, 1959 to O. R. Ethridge); 2,940,876 (issued Jun. 14, 1960
to N. E. Elsas); 3,133,836 (issued May 19, 1964 to U. L. Winfrey); and
3,234,046 issued Feb. 8, 1966) to G. R. Etchison). This more effective
dispersion by jet-cooking provides a lower in-process viscosity, without
degradation, than other cooking methods. This allows the use of lower
cooking and conveying temperature and pressure which further assists in
reducing degradation.
Therefore, there is a need for a spray-drying process which converts
crystalline polymers to a substantially amorphous, i.e., "glassed" form,
without substantial degradation by thoroughly cooking and drying
water-dispersible or water-soluble natural polymers, such as unconverted
starches and gums, or synthetic polymers such as polyvinyl alcohol at
commercially acceptable solids concentration.
There is also a long felt need for a cooking and drying process that
transforms cold-water-insoluble, partially insoluble, or slow to hydrate
polymers (natural or synthetic) into new spray-dried powder forms which
disperse in cold water and are substantially non-crystalline,
non-retrograded and non-degraded by the Process. The prior art teaches
many methods that produce pre-dispersed polymers, but the resulting
polymers do not posses the full range of desired properties. There is a
need for a spray-drying process which thoroughly cooks and dries
crystalline polymers, such as converted starches, at higher solids than is
currently possible.
In particular, there is a need for the following:
i) pregelatinized, spray-dried, fully pre-dispersed high amylose starches
(modified or unmodified) which disperses in water (i.e., high amylose
starches which are substantially cold-water-soluble and completely
hot-water-soluble) and whose redispersions give strong gels with improved
textural properties;
ii) fully pre-dispersed, spray-dried forms of modified or unmodified
natural gums (which are inherently poorly dispersible due to crystalline
or associated regions), especially polygalactomannan gums whose backbones
are more linear in nature and have a tendency to associate to form
crystalline regions, such as locust bean gum, and whose spray-dried forms
yield cold-water redispersions with the solution properties of the parent
gum.
iii) fully pre-dispersed, spray-dried forms of synthetic polymers which are
inherently poorly dispersible due to crystalline or associated regions,
especially substantially fully hydrolyzed polyvinyl alcohols and whose
spray-dried forms yield cold-water redispersions with the solution
properties of the parent polymer.
SUMMARY OF THE INVENTION
The coupled jet-cooking/spray-drying process described herein is a
continuous process for jet-cooking and spray-drying an inherently
water-dispersible or water-soluble polymer which is insoluble in cold
water because of the presence of crystalline regions and which can be
disoriented by heating, yielding a dispersion or solution which is low in
viscosity at elevated temperatures. The process comprises the steps of:
(a) forming a slurry or a paste comprising the polymer and water;
(b) jet-cooking the aqueous slurry or paste of the polymer with steam at a
temperature sufficient to fully disperse or solubilize the polymer;
(c) immediately conveying and introducing under elevated temperature and
pressure the jet-cooked dispersion or solution into a nozzle of a
spray-dryer chamber;
(d) atomizing the jet-cooked dispersion or solution through the nozzle of
the spray-dryer;
(e) drying the atomized mist of the jet-cooked polymer within the
spray-dryer chamber; and
(f) recovering the jet-cooked and spray-dried polymer as a
water-dispersible or water-soluble powder.
The cooking temperature used will depend upon the polymer The use of too
high a cooking temperature may degrade a polymer such as starch. Suitable
temperatures are about 93.degree.-177.degree. C. (200.degree.-350.degree.
F.) for most polymers, 138.degree.-177.degree. C. (280.degree.-350.degree.
F.) for starches containing about 70% amylose, 121.degree.-162.degree. C.
(250.degree.-325.degree. F.) for starches containing less than about 40%
amylose, 104.degree.-149.degree. C. (220.degree.-300.degree. F.) for low
viscosity cold-water soluble starches, 99.degree.-163.degree. C.
(210.degree.-325.degree. F.) for fully hydrolyzed polyvinyl alcohol and
93.degree.-163.degree. C. (200.degree.-325.degree. F.) for natural gums.
The cooking chamber pressure used in the continuous coupled process is low,
typically 20 to 130 psig, and is the saturation pressure of steam at the
temperature used plus the small incremental pressure needed to move the
dispersion through the chamber. Cooking chamber pressures suitable for
high amylose starches are 80 to 150 psig, most preferably 100 to 130 psig
for a starch having an amylose content of about 70%.
Excessive shear, like too high a cooking temperature, will degrade a
polymer such as starch and should be avoided unless a converted (i.e.,
degraded) starch is desired.
An essential step in the present process is the conveying of the thoroughly
cooked, substantially fully dispersed polymer, under elevated pressure and
temperature, to the spray-dryer atomization nozzle. In the preferred
method, a low shear pneumatic nozzle is used, and the transfer is carried
out at substantially the same temperature and pressure used in the
jet-cooking. The transfer is carried out without any venting to the
atmosphere. A pressure nozzle can be used for atomization. However, its
use adds operational complexity to the Process and may shear the
dispersion, thus producing a degraded product.
One of the advantages of the coupled jet-cooking/spray-drying process is
that it produces a fully pre-dispersed polymer, processed without
substantial degradation and dried without substantial retrogradation or
reassociation, which maximizes useful properties. The spray-dried powders
redisperse in water to give dispersions with unexpected smooth textures
and high viscosities or strong gel strengths.
Another advantage of the present continuous coupled process is that
hydrolyzed starches having a water fluidity (W.F.) of about 80, which are
conventionally spray-dried at 27% solids, are easily processed at 38%
solids. Thus, the present process is limited only by the viscosity of the
feed into the jet-cooker.
A further advantage of the present process is that low solids are not
required for proper atomization of starches of higher viscosity. Prior art
conventional processes with separated cooking and spray-drying steps are
less advantageous when atomizable viscosities can only be obtained at low
solids. In those two step processes, with 70% amylose starch, the cooled
starch dispersion at atmospheric pressure is too viscous to spray-dry due
to retrogradation or gel formation if the solids content of the starch
slurry is above 10% solids. In the continuous coupled,
jet-cooking/spray-drying process the thoroughly cooked, hot dispersion is
only slightly more viscous than water, even when the solids are 25%, and
hence the dispersion can be easily spray-dried.
One disadvantage of cooking the starch slurry in a tubular heat exchanger,
such as that used by Winkler in the examples of U.S. Pat. No. 3,630,775
(discussed in the Background) is the higher temperature required since the
slurry is indirectly heated rather than directly heated as with
jet-cooking. The processing conditions used by Winkler in the high amylose
starch example suggest that there were difficulties in dispersing the
starch since the lowest percent solids, highest temperature and longest
dwell time were used during cooking. Another disadvantage is the high
pressure (above 1000 psi) required to transport the less than optimally
dispersed starch through the heat exchanger and to atomize the dispersion
using a single fluid pressure nozzle. A single fluid pressure nozzle is an
extremely high shear atomization device which can cause molecular
breakdown of high solids starch dispersions, hence altering viscosity and
functionality. In contrast, in the continuous coupled
jet-cooking/spray-drying process, the operating pressure when the
preferred pneumatic nozzle is used is less than 150 psig. Atomization is
thus accomplished with less shear and minimum degradation results, thus
maintaining viscosity or gelling properties of the original polymer. See
Example XI which compares starches cooked in an heat exchanger and
atomized through a single fluid pressure nozzle with starches cooked in a
jet-cooker and atomized through a pneumatic nozzle.
All of the starches which are pregelatinized using the present process can
be prepared in the form of fully pre-dispersed, non-granular starches
which are substantially non-crystalline (i.e., they are amorphous
"glassed" solids). The jet-cooked dispersions are fully dispersed and do
not contain granules or granular fragments; they are fully dispersed. Such
pregelatinized starches are highly water-soluble and substantially
non-degraded, i.e., the molecular weight of the processed starch is not
substantially less than that of the unprocessed base starch. When the
starch base is other than a high amylose starch, such as corn, tapioca,
potato, waxy maize, and the like, the resulting pregelatinized starch
powder is completely cold-water-soluble (CWS). When the starch base is a
high amylose starch, the resulting pregelatinized starch powder is very
soluble. For example, a hybrid corn starch having an amylose content of
about 70% processed by the present process has cold and hot water
solubilities of about 70% and 99%, respectively. These pregelatinized high
amylose starch powders give high viscosity solutions when redispersed in
hot water. The split second drying time during processing minimizes
association through hydrogen bonding so that the resulting starches are
substantially non-retrograded.
The unique spray-dried pregelatinized high amylose starches and their
mixtures with other starches prepared by the present process form strong
gels when redispersed in hot water (90.degree.-100.degree.
C.--194.degree.-212.degree. F.) and cooked in a boiling water bath for 15
minutes. The gel strength is about 230-240 g/cm.sup.2 at 6% solids for a
high amylose starch containing about 70% amylose, which is equivalent to
the maximum gel strength obtained when the same starch is jet-cooked
independently under optimum cooking conditions). Strong gels are also
formed when these pregelatinized starches are redispersed in cold water
(25.degree. C.-77.degree. F.) and not cooked (150-160 g/cm.sup.2 at 6%
solids for a high amylose starch containing about 70% amylose). As is
shown in Example XI, the starch is not degraded as is the starch
pregelatinized using the Winkler process (see U.S. Pat. No. 3,630,775
discussed in the Background). A spray-dried starch having an amylose
content of about 70% which is pregelatinized using the present coupled
process has an intrinsic viscosity between 0.7-0.9. The intrinsic
viscosity of the non-processed base is typically between 0.9-1.0. This
demonstrates that the present process produces a substantially
non-degraded starch since the molecular weight of the processed starch is
similar to that of the base starch from which it is derived.
Typical high amylose starches include those having an amylose content of
about 100% (e.g., isolated potato amylose) or 40-70% (e.g., corn hybrids)
and the starch may be modified by derivatization, conversion, or
complexing. Modification by crosslinking is possible but not desirable as
the advantage of the present process is the preparation of soluble
starches. Lightly crosslinked starches that can be fully dispersed are
suitable, whereas heavily crosslinked starches that are not fully
dispersed during cooking are not suitable.
The starches prepared by the coupled process are amorphous white powders
with particles having the shape typical of spray-dried starches, i.e. a
convoluted indented sphere. However, unlike other conventionally
spray-dried non-granular high amylose starches processed at low solids,
the high amylose starch is substantially fully and completely disorganized
as evidenced by amorphous X-ray patterns, substantially non-retrograded as
evidenced by amorphous X-ray patterns and optimum gel strengths, and
substantially non-degraded as evidenced by intrinsic viscosities that are
similar to the base starch.
The high amylose starches prepared by the present coupled
jet-cooking/spray-drying process are more completely dispersed than those
prepared by the autoclaving and drum-drying process of Sarko, U.S. Pat.
No. 3,086,890 (discussed in the Background). This is evidenced by the
significantly higher gel strengths. For example, the pregelatinized starch
having an amylose content of about 70% prepared by the continuous coupled
jet-cooking/spray-drying process has a gel strength of about 160
g./cm..sup.2 when redispersed in hot water at 6% solids, while the same
base starch prepared by jet-cooking and drum-drying has a gel strength of
only about 110 g./cm..sup.2 when redispersed in hot water at 6% solids.
This difference in gel strength is unexpected and an indication that the
coupled continuous process produces a different product, i.e., a
substantially fully disorganized and non-retrograded product. The
autoclaving and drum-drying process of Sarko uses, as a starting material,
a previously processed starch fraction (isolated amylose) which is
prepared by high temperature cooking, precipitation of the desired
fraction, and recovery by drying. In the present process, isolated starch
fractions are usable, but native (non-cooked) starches are preferred.
The high amylose starch powders prepared by the coupled
jet-cooking/spray-drying process are significantly more dense than
pregelatinized starches prepared using a conventional two step process
which involves jet-cooking and then spray-drying a low solids aqueous
dispersion of the jet-cooked starch, as shown in example XIII and
discussed in Example XIV. The high amylose starch powders obtained herein
also form a significantly firmer gel (about 200 versus 45-90 g./cm..sup.2
at 6% solids when redispersed in hot water).
The high amylose starch powders and other starch powders prepared by the
coupled jet-cooking/spray-drying process are completely non-granular
unlike the pregelatinized starches prepared by cooking the starch in an
atomized state. As described in U.S. Pat. No. 4,280,851 (discussed in the
Background), the simultaneously cooked and spray-dried starches are
uniformly gelatinized granules in the form of indented spheres with a
majority of the granules being whole and unbroken and swelling upon
rehydration. In attempting to carry out this process with a high amylose
starch (about 70% amylose), we have observed that it is difficult to
prepare a highly soluble product. The high amylose starch is resistant to
gelatinization under the processing conditions described in this reference
.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the high temperature viscometer, a measurement device used to
carry out the high-temperature flow rate viscosity measurement.
FIG. 2A shows a X-ray crystallographic scan for a high amylose starch
(about 70% amylose) pregelatinized by the present continuous coupled
jet-cooking/spray-drying process.
FIG. 2B shows a X-ray crystallographic scan for a high amylose starch
(about 70% amylose) pregelatinized by jet-cooking and drying on a heated
plate.
FIG. 2C shows a X-ray crystallographic scan for a high amylose starch
(about 70% amylose) pregelatinized by jet-cooking and air-drying (see
Curve C).
FIG. 3 compares the gel strengths of spray-dried high amylose starches
(about 70% amylose) pregelatinized using the present continuous, low
shear, direct heating process which couples a jet-cooker with a
spray-dryer having a pneumatic-type nozzle and the cook of the continuous,
high shear, indirect heating process exemplified by Winkler in U.S. Pat.
No. 3,630,775 which couples a tubular heat exchanger and a spray-dryer
using a single fluid high pressure nozzle.
FIG. 4 compares the viscosities of waxy corn starch, pregelatinized using
the present continuous, low shear, direct heating process which couples a
jet-cooker with a spray-dryer having a pneumatic-type nozzle, and the cook
of the continuous, high shear, indirect heating process exemplified by
Winkler in U.S. Pat. No. 3,630,775 which couples a tubular heat exchanger
and a spray-dryer using a single fluid pressure nozzle.
FIG. 5 compares the viscosities of corn starch pregelatinized using the
present continuous, low shear, direct heating process which couples a
jet-cooker with a spray-dryer having a pneumatic-type nozzle and the cook
of the continuous, high shear, indirect heating process exemplified by
Winkler in U.S. Pat. No. 3,630,775 which couples a tubular heat exchanger
and a spray-dryer using a single fluid high pressure nozzle.
FIG. 6A presents scanning electron microscope photomicrograph of the fully
dispersed, non-granular pregelatinized high amylose starch prepared by the
continuous coupled jet-cooking/spray-drying process.
FIG. 6B presents a scanning electron microscope photomicrograph of the
granular, spray-dried particles of pregelatinized high amylose starch
prepared by the simultaneous atomization and cooking process of Winkler
(U.S. Pat. No. 4,280,851).
FIG. 6C presents a scanning electron microscope photomicrograph the
pregelatinized high amylose starch prepared by the
jet-cooking/drum-drying, a process similar to that of Sarko (U.S. Pat. No.
3,086,890).
FIG. 7 compares the displacement density and bulk density of various
pregelatinized starches (potato amylose, high amylose corn, Potato, corn,
tapioca and waxy maize) prepared by the continuous coupled
jet-cooking/spray-drying process, a conventional spray-drying process, and
the jet-cooking/drum-drying, a Process similar to that of Sarko (U.S. Pat.
No. 3,086,890).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used herein, the term "crystalline" polymer refers to any natural or
synthetic polymer which contains crystalline regions or domains which must
be disorganized to render the polymer amorphous and hence dispersible or
soluble in cold water. Suitable polymers for use in the present process
are those which develop a high viscosity after dispersion in hot water and
whose aqueous dispersions have a reduced viscosity at elevated
temperatures. Suitable natural polymers include water-dispersible or
water-soluble polysaccharides such as starches, gums and cellulose
derivatives. Suitable synthetic polymers include polymers such as fully
hydrolyzed, medium to very high molecular weight polyvinyl alcohols.
Any cookable, granular unmodified or modified starch or previously cooked
starch (including those not fully dispersed) other than a highly
crosslinked starch is suitable as a starting material for use in the
present process. Different types of suitable base starches include those
from cereal grains, such as corn, milo, wheat and rice; those from tubers,
such as potato, tapioca, and arrowroot; and those that are waxy starches,
such as waxy milo, wavy maize, and waxy rice.
As used herein, the term "high amylose starch" refers to starches from any
starch base which contain concentrations of at least about 40% amylose,
including, for example, high amylose corn, wrinkled pea, and 100% amylose
isolated from a starch such as potato starch. It also refers to mixtures
of a high amylose starch and starches having an amylose content below 40%,
such as waxy maize, corn, tapioca, potato, rice and the like. The mixtures
can be processed and yield a mixed powder with good gelling properties,
provided the mixture has a total amylose content of at least 35%. The
preferred high amylose starches are those derived from high amylose corn
hybrids.
Jet-cooking is a conventional process which involves the instantaneous
heating of a flowing liquid (in the present process an aqueous suspension,
also referred to as a slurry or paste) with a hot condensable vapor (in
the present process steam) and holding the heated liquid at a selected
temperature for a selected time. Various apparatus suitable for
jet-cooking are referred to in the Background. Suitable cookers are
available from National Starch and Chemical Corp. (United States), Avebe
(Holland), or Roquette Freres (France).
Spray-drying is likewise a conventional process and described in Spray
Drying: An Introduction to Principles, Operational Practice and
Applications by K. Masters, published in 1972 by Leonard Hill Books, a
division of International Textbook Co Ltd., London. Spray-dryer nozzles
suitable for use herein include pressure nozzles and pneumatic-type
nozzles such as two-fluid nozzles.
In a pneumatic nozzle, the liquid to be atomized (here the cooked polymer
dispersion) and an atomizing gas (air or steam) are fed separately to the
nozzle at pressures generally between 50 psig and 200 psig. Atomization is
effected by impinging the pressurized atomizing gas on a stream of the
liquid at a velocity sufficient to break the stream into droplets. In the
present invention, pressure (and the resulting velocity) of the atomizing
as must be sufficient for propert atomization into small droplets to allow
rapid drying to an appropriate residual moisture without retrogradation or
reassociation. Use of pneumatic nozzles is preferred in the coupled
jet-cooking/spray-drying process due to the low operating pressures
(similar to those needed for jet-cooking) and the low shear on the feed
inherent in this design. Pneumatic nozzles are discussed in greater detail
on pages 16 f of Master's book cited above.
Pressure nozzles may also be used for atomization. Atomization, in a
pressure nozzle, is effected by inducing rotation in the liquid and
passing it through a small orifice. The liquid, on exiting the orifice,
forms a cone-shaped film which is unstable, breaking into droplets. Use of
a pressure nozzle in the present process requires insertion of a high
pressure pump (2,000 to 10,000 psig) between the jet-cooker and the
atomization nozzle. The temperature after passage through the high
pressure pump should be maintained substantially equivalent to the
jet-cooking chamber temperature. The pressure after the high pressure pump
must be sufficient to properly atomize the dispersion into small droplets
to allow rapid drying to an appropriate residual moisture without
retrogradation or reassociation. Use of a pressure nozzle adds operational
complexity to the present process and may shear the dispersion, thus
producing a degraded product. Suitable pressure nozzles are also described
in the Masters reference cited above.
For example, in the present process a starch slurry (up to 38% anhydrous
basis) is prepared. The starch slurry is then directed through a cooking
chamber, mixed with high temperature steam (at 80-150 psig), and
gelatinized in a continuous jet-cooker. The starch is cooked at a solids
and temperature sufficient to reduce its viscosity at elevated temperature
to a low range (near that of water), without significant degradation.
The exit of the cooking chamber is connected to a spray-nozzle, preferably
a pneumatic-type spray-nozzle, situated in a spray-dryer. The starch cook,
while still at a high temperature and low viscosity, is directed into the
spray-nozzle and atomized with cold air, hot air or steam. Once the hot
jet-cook has been atomized, it is handled in the same manner as
conventional spray-dried starches.
The continuous coupled process is economical. It provides high flow rates
through a given spray-dryer orifice at high starch solids but at pressures
that are low enough to minimize degradation of the starch.
The coupled process is versatile. The processing equipment may be arranged
to optionally add other materials during the jet-cooking step. For
example, (1) a water-soluble compound such as sugar or a water-dispersible
compound such as a gum can be added to a starch slurry and a spray-dried
mixed powder obtained; (2) a water-insoluble compound, such as an oil, can
be added to the starch and a starch powder containing encapsulated oil
obtained; (3) a complexing agent such as a surfactant can be added to a
starch slurry and a starch-surfactant complex obtained; (4) an acid may be
added to the slurry and an acid-converted starch product obtained; or (5)
a derivatizing agent may be added to the slurry and a derivatized starch
product obtained. The processing equipment can also be arranged to provide
for post-drying treatments such as the agglomeration of the starch powder,
or a heat-moisture treatment of the starch powder.
The above procedure (encapsulation, complexation, conversion,
derivatization, agglomeration, and heat treatment) are well-known starch
modifications and described, for example, in Chapter 22: Starch and Its
Modification by M. W. Rutenberg in Handbook of Water-Soluble Gums and
Resins, edited by Robert L. Davidson and published by McGraw Hill Book
Co., New York 1980 or in the patent literature.
Jet-cooks of a high amylose starch (about 70% amylose) maintained at
temperatures from 126.degree.-153.degree. C. (259.degree.-307.degree. F.)
flow through spray-drying nozzles at rates no less than half that of
water, even at a 28% cook solids. This translates into a flow viscosity of
less than 1 centipoise at temperatures of 109.degree.-145.degree. C.
(228.degree.-293.degree. F.). The viscosity of a 28% solids jet-cook of
the same starch cannot be measured after it exits the cooker and drops in
temperature to below 100.degree. C. (212.degree. F.) since it forms a gel
in a few seconds. Therefore, flow rates are measured instead of viscosity.
Accurate viscosity measurements of non-Newtonian liquids such as starch
cooks are very difficult to measure.
Starch cook viscosities (by flow rate comparison with water) decrease with
increasing temperature, decreasing molecular weight, decreasing solids,
and increasing amylose content (e.g., a high amylose starch having an
amylose content of about 50% is more viscous than a high amylose starch
having an amylose content of about 70%).
In the examples which follow, all temperatures are in degrees Celsuis and
Fahrenheit. All spray-drying nozzles are obtainable from Spray Systems
Co., Wheaton, Ill. The following test procedures were used.
WATER SOLUBILITY
A. Cold Water Solubility
The determination is carried out using distilled water at room temperature.
About 0.5 g. of starch is dispersed in 30-40 ml. of water in a semi-micro
stainless steel cup on a Waring blender base (Model 31B292). The blender
is run at low speed while the starch is added (all at once) and then run
at high speed for 2 minutes. The dispersion is immediately transferred to
a 50 ml. volumetric flask and diluted to 50 ml. with water. A 25 ml.
portion of the stock dispersion (shaken well to ensure a homogenous
dispersion) is removed by pipet and transferred to a 50 ml. centrifuge
tube. The sample is spun down at 1800-2000 RPM for 15 minutes. Once spun
down, 12.5 ml. of supernatant is pipetted into a 25 ml. volumetric flask,
5 ml. of 5N potassium hydroxide (KOH) are added with swirling, and the
mixture is diluted with water. The remainder of the stock dispersion is
shaken well, the insoluble starch dispersed with 10 ml. of 5N KOH while
swirling. The mixture is diluted to 50 ml. with water. The optical
rotation of both the concentrated stock solution (B) and the supernatant
solution (A) is measured.
##EQU1##
B. Hot Water Solubility
The procedure is the same as that described above except that boiling
distilled water at 90.degree.-100.degree. C. (194.degree.-212.degree. F.)
is used for dispersing the starch and all subsequent dilutions. No attempt
is made to maintain temperature during the procedure.
FLUIDITY MEASUREMENTS
A. Water Fluidity (W.F.)
This test is described in U.S. Pat. No. 4,207,355 issued Jun. 10, 1980 to
C. W. Chiu et. al., the disclosure of which is incorporated herein by
reference.
B. Calcium Chloride Viscosity (7.2% Solids Test)
The calcium chloride viscosity of the converted high amylose starch is
measured using a Thomas Rotation Shear-Type Viscometer standardized at
30.degree. C. (86.degree. F.) with a standard oil having a viscosity of
24.73 cps., which oil requires 23.12.+-.0.05 seconds for 100 revolutions.
As the conversion of the starch increases, the viscosity of the starch
decreases and the calcium chloride viscosity decreases. Accurate and
reproducible measurements of the calcium chloride viscosity are obtained
by determining the time which elapses for 100 revolutions at a specific
solids level.
A total of 7.2 g. of the converted starch (anhydrous basis) is slurried in
100 g. of buffered 20% calcium chloride solution in a covered semi-micro
stainless steel cup (250 ml. capacity available from Eberbach), and the
slurry is transferred to a glass beaker and is heated in a boiling water
bath for 30 minutes with occasional stirring. The starch solution is then
brought to the final weight (107.2 g.) with hot (approximately
90.degree.-100.degree. C.--194.degree.-212.degree. F.) distilled water.
The time required for 100 revolutions of the resultant solution at
81.degree.-83.degree. C. (178.degree.-181.degree. F.) is measured three
times in rapid succession and the average of the three measurements is
recorded.
The calcium chloride solution is prepared by dissolving 264.8 g. of reagent
grade calcium chloride dihydrate in 650 ml. of distilled water in a tared
1 l. glass beaker. Thereafter 7.2 9. of anhydrous sodium acetate is
dissolved in the solution. The solution is allowed to cool and the pH is
measured. If necessary, the solution is adjusted with hydrochloric acid to
pH 5.6.+-.0.1. The solution is then brought to weight (1007.2 g.) with
distilled water.
GEL STRENGTH
A gel is prepared by dispersing a starch sample (on an anhydrous basis) in
boiling distilled water (approximately 90.degree.-100.degree.
C.--194.degree.-212.degree. F.) at appropriate solids in a Waring blender
(Model 31B292) set at low speed for 2 minutes, transferring to a glass
beaker, then cooking the sample in a boiling water bath for 15 minutes.
The sample is brought back to weight with boiling distilled water and is
then placed in a jar covered with a lid and allowed to cool undisturbed
for 24 hours at 21.degree. C. (70.degree. F.) to gel. Unless stated
otherwise, all gels are prepared in boiling water and cooked as stated
above. For cold water gel strengths, the gel is made in room temperature
(25.degree. C.--77.degree. F.) distilled water without cooking. The
strength is measured using a Stevens LFRA Texture Analyzer (available
through Texture Technologies Corp , Scarsdale, N.Y.) employing a 0.25 in.
diameter cylindrical probe, run at a speed of 0.5 mm./sec. The force in
g./cm..sup.2 required for the probe to penetrate the gel a distance of 4
mm. is measured three times and the average is recorded. The solids and
probe selection are varied according to the starch type. For example, all
high amylose corn starches (about 70% amylose) and isolated potato amylose
(about 100% amylose) were tested with a 0.25 in. diameter cylindrical
probe at 6% solids (dry basis). Unless stated otherwise, these conditions
can be assumed.
BROOKFIELD VISCOSITY
Brookfield viscosity is measured using a RVF Brookfield viscometer
(available through Brookfield Engineering Laboratories, Inc., Stoughton,
Mass.) and an appropriate spindle at 20 rpm. The instrument is allowed to
rotate five times before a reading is taken. All viscosity readings are
run at 22.degree. C. (72.degree. F.), and all test dispersions are
prepared using the above gel strength procedure unless stated otherwise.
INTRINSIC VISCOSITY DETERMINATION
The intrinsic viscosity of starch is measured by quantitatively
transferring 2.500 g..+-.0.001 g. of anhydrous starch into a 600 ml.
beaker containing about 250 mls. of distilled water at about 25.degree. C.
(77.degree. F.). Then 100 mls. of 5N.+-.0 05N KOH solution are pipetted
into the beaker, and the mixture is stirred for 30 minutes on a stir
plate. This solution is clear and does not contain undissolved starch. The
flask and is brought to volume with distilled water. The solution is
quantitatively transferred to a 500 ml. volumetric solution is filtered
through a funnel packed with glass wool. Then 40.0, 30.0, 20.0 and 10.0
mls. of this solution are pipetted into 50 ml. volumetric flasks and
brought to volume with 1N.+-.0.10N KOH solution. The flow times for each
concentration (0.40, 0.30, 0.20 and 0.10% solids plus the stock solution
at 0.50% solids) and the flow time of the 1N KOH solution is determined in
a Cannon-Fenske Viscometer (No. 100, 45-65 seconds flow time for water at
35.degree. C.) mounted in a constant temperature bath maintained at
35.00.degree..+-.0.02.degree. C. The flow times for each dilution are run
in triplicate. The intrinsic viscosity is the point at which the
extrapolated line of a plot of N.sub.sp /concentration (y-axis) versus
concentration (x-axis) intercepts the y-axis. N.sub.sp =N.sub.rel -1 and
##EQU2##
VISCOSITY BY FLOW-RATE MEASUREMENT
The device used for high-temperature flow-rate viscosity measurement is
shown in FIG. 1. It is used to measure the flow rate of fluids under high
temperature/pressure conditions. A jet-cooker is used to raise the
temperature/pressure of these fluids. The high temperature starch cook
viscosity is determined by comparing its flow rate to that of water under
identical conditions. Solids concentration are stated in the Examples.
The "small" nozzle orifice, which has an opening of 0.016 in., is used for
low solids cooks (spraying systems fluid cap 40100). The "large" nozzle
orifice, which has an opening of 0.031 in., is used for high solids cooks
(fluid cap 600100).
A. Cooked Starch Flow Rate Measurement
The starch is slurried in water at the desired solids and adjusted to
approximately pH 6 with dilute sulfuric acid or sodium hydroxide as
required. The slurry is then jet-cooked at temperatures between
149.degree.-155.degree. C. (300.degree.-311.degree. F.). The starch cook
is then directed (while kept at temperature) into an insulated steel
chamber fitted with a spray-drying nozzle and an overflow line to flash
off excess steam and to control pressure. The valve opening to the
overflow line is adjusted to bring the pressure and thus the temperature
to the desired point and to eliminate any excess steam. Gases (steam) in
the liquid stream cause an uneven flow ("spitting") and must be eliminated
to provide accurate flow results. Once the pressure/temperature have been
adjusted and steam has been eliminated, a valve is opened to allow flow
through the spray-drying orifice while maintaining constant pressure.
Simultaneously, a graduated cylinder is placed under the orifice and a
timer is started. A sample is collected for approximately 30 seconds, from
which the flow rate per minute is calculated. Water is run through this
procedure and is used as the standard for comparison.
B. Water Flow Rate Measurement
Water was run at 20, 40 and 60 psig of pressure to obtain temperatures of
126.degree., 142.degree., and 153.degree. C. (259.degree., 287.degree.,
307.degree. F.) using the procedure given above. The results are shown
below:
______________________________________
Orifice Temperature
Flow
Size Pressure of Fluid Rate
(in.) (psig) .degree.C. (.degree.F.)
(ml./minute)
______________________________________
0.016 20 126 (259) 100
0.016 40 142 (287) 138
0.016 60 153 (307) 180
0.031 20 126 (259) 360
0.031 40 142 (287) 600
0.031 60 153 (307) 699
______________________________________
POWDER DENSITY
A) Bulk Density
A tared 100 cc. graduated cylinder is filled to the 100 cc. mark with "as
is" test sample powder. The cylinder is tapped on a hard surface until no
further drop in volume is noted.
##EQU3##
B) Displacement Density
A Hubbard-Carmick, 25 ml. capacity, specific gravity bottle is tared and a
small amount of anhydrous glycerin is added to wet out the bottom of the
bottle. A known amount of starch (about 5 g. "as is") is weighed into the
bottle and the bottle is filled about half way with more glycerin. After
mixing, the bottle is filled within 1/4 to 1/8 inch of the top with
glycerin and placed under a vacuum until all air bubbles are dissipated.
Glycerine is added to completely fill the bottle and the total weight is
taken. The procedure is run with glycerin alone (no starch) to determine
the volume of the bottle. All work must be done at 25.degree. C.
(77.degree. F.).
##EQU4##
EXAMPLE I
This example shows the preparation of pregelatinized non-granular high
amylose corn starches (about 70% amylose).
PART A--PREPARATION AT LOWER COOK SOLIDS (13%)
An unmodified granular high amylose starch was slurried in water and pumped
using a gear pump into a jet-cooker. Steam (at 145 psig) was metered into
the slurry stream and the starch was cooked. The hot starch cook was
conveyed at a temperature and pressure only slightly reduced from the
cooking chamber to a pneumatic atomization nozzle bottom mounted in a
spray-dryer. Compressed air was used to atomize the starch. Hot air in
counter-current flow was used to dry the atomized starch mist. The
resulting powders were recovered in a cyclone separator. The process
variables used are shown in Table I. The spray-dryer is a laboratory Model
No. 1 Anhydro spray-dryer.
The effect of cooking shear on the gel strength of starch powders
redispersed at 6% solids in hot water is shown. The shear was varied by
varying the amount of gaseous steam present in the starch cook as it moved
through the cooker. At lower shear levels (20.0 g./min. of steam flow),
the starch was not thoroughly and efficiently cooked, and this was
reflected in less than maximum gel strength (194 g./cm..sup.2) (see Column
1). At optimum shear levels for this system (24.0 g./min. steam flow) a
maximum gel strength of 215 g./cm..sup.2 was achieved. Increasing the
shear by using a steam flow of 36 or 62 g./min. resulted in lower gel
strengths (204 and 134 g/cm..sup.2) (see columns 3 and 4). Proper shear
must be determined experimentally and it will depend on the starch used,
the hydraulic characteristics of the cooking and atomizing equipment used,
and the cooking temperature, as well as the gel strength required for the
desired end use.
PART B--PREPARATION AT HIGHER COOK SOLIDS (28%)
The process variables used for jet-cooking/spray-drying in larger scale
equipment at higher solids are shown in Column 5 of Table 1. The slurry of
unmodified granular high amylose starch was fed into a jet-cooker (Model
C-15 available from National Starch and Chemical Corp). Steam was metered
into the slurry as above. The cooked starch was conveyed to a pneumatic
atomization nozzle top mounted in a 35 ft. tall, 16 ft. diameter Hensey
spray-dryer. Steam at 120 psig was used to atomize the starch. The
atomized starch mist was dried with air at 204.degree. C. (400.degree.
F.).
The cold water solubility of the above non-granular starch powders was
97.4% and the hot water solubility was greater than 99%.
The types of pneumatic nozzle set-ups used in the spray-dryers are
indicated in the Table and available from Spraying System Inc.
EXAMPLE II
This example demonstrates the processing of a converted high amylose corn
starch (about 70% amylose) using the coupled jet-cooking/spray-drying
process. A slurry of the starch was treated with 2.5% hydrochloric acid at
52.degree. C. (126.degree. F.) for 16 hours to give a converted starch
having a calcium chloride viscosity of 25 seconds. After neutralization
with sodium carbonate to a pH of about 6, the granular converted starch
was filtered, washed and dried. The starch was then jet-cooked using the
following conditions: 21% cook solids, 143.degree. C. (290.degree. F.)
cooking temperature, 27 g./min. steam flow, and 39.7 ml./min. cooking
rate. The jet-cooked starch dispersion was spray-dried through a two-fluid
Spray Systems nozzle (set-up 22) into a Niro Utility #1 spray-dryer. The
inlet temperature was 250.degree. C. (428.degree. F.) and the outlet
temperature was 88.degree. C. (190.degree. F.) The starch powder was 93.0%
soluble in cold-water and 97.1% soluble in hot-water.
EXAMPLE III
This example demonstrates that a blend of a high amylose corn starch and
another starch can be processed using the coupled jet-cooking/spray-drying
process. About 35 parts of a converted high amylose corn starch (about 70%
amylose and calcium chloride viscosity of about 25 seconds) was slurried
with about 65 parts of a converted corn starch (about 28% amylose and
water fluidity of 65) in 150 parts of water. The following jet-cooking
conditions were used: 23% cook solids, 143.degree. C. (290.degree. F.)
cooking temperature, 27.5 g./min. steam flow, and 39 ml./min. cooking
rate. The jet-cooked starch dispersion was spray-dried through a two-fluid
Spray Systems nozzle (set-up 22B) into an Anhydro laboratory Model No. 1
spray-dryer. The inlet temperature was 230.degree. C. (446.degree. F.) and
the outlet temperature was 86.degree. C. (187.degree. F.) .
The resulting non-granular starch powder was 95.1% soluble in cold water
and greater than 99% soluble in hot water. On redispersion in hot water at
6% solids it formed a gel having a strength of 42 g./cm..sup.2. The
fluidity corn starch processed under similar conditions did not gel. The
fluidity high amylose corn starch processed under similar conditions
formed a gel having a strength of 75-85 gm./cm..sup.2. The results show
that the co-processed blend provided a starch powder which formed a gel.
EXAMPLE IV
This example demonstrates that a mixture of a granular unmodified high
amylose corn starch (about 70% amylose) and fructose or sorbitol can be
processed using the coupled jet-cooking/spray-drying process.
The processing conditions and results were as follows:
__________________________________________________________________________
Typical High
87.5% High
92.5% High
Amylose Amylose Amylose
Starch Starch + 12.5%
Starch + 7.5%
Conditions (Comparative)
Fructose
Sorbitol
__________________________________________________________________________
Cook solids (%)
15-16 14.5 14.0
Cooking temperature (.degree.C.(.degree.F.))
143 (290)
143 (290)
143 (290)
Steam flow (g./min.)
27.5 27.5 27.5
Cooking rate (ml./min.)
24-36 35.0 35.0
Spray-dryer Anhydro Anhydro Anhydro
Inlet temperature (.degree.C. (.degree.F.)
240 (464)
220 (428)
230 (446)
Outlet temperature (.degree.C. (.degree.F.)
90 (194)
82 (180)
84 (183)
Two fluid nozzle set-up
22B 22B 22B
Cold water solubility (%)
71.4 64.9 96.6
Hot water solubility (%)
94.5 83.7 80.3
Gel strength at 6% solids
220 119.0 172.0
(g./cm..sup.2)
__________________________________________________________________________
The results show that co-processed powdered mixtures were highly soluble
(64.9 and 96.6%) in cold water and formed strong gels (119 and 172
g./cm..sup.2) even though they contained lower starch solids than the
comparative sample.
EXAMPLE V
This example describes the production and recovery of a derivatized starch
using the coupled jet-cooking/spray-drying process.
A starch is slurried in water and the pH is adjusted to between pH 6 and pH
8 with sulfuric acid or sodium hydroxide as required. An aqueous sodium
tripolyphosphate (STP) solution is added either to the bulk starch slurry
or metered into the starch feed line prior to the jet-cooker at a level
sufficient to give 1 to 4% STP on starch. The starch/STP slurry is
jet-cooked at a temperature 163.degree.-177.degree. C.
(325.degree.-350.degree. F.).
This modified starch dispersion is conveyed, at temperature and pressure
substantially equivalent to those used during cooking directly to an
atomization nozzle mounted in a spray-dryer. After atomization and drying
the resulting powder is collected.
It is expected that the recovered starch powder will have the properties of
a conventional starch phosphate produced by slurry reaction. In addition,
it is expected that the powder will be readily water-soluble and not
require cooking to produce a functional water dispersion. Reactions on
cooked starches are known but yield liquid Products and have generally
been avoided due to difficulty in recovering the viscous reaction products
or expense in recovering low solids cooks. For example, U.S. Pat. No.
3,637,656 (issued Jan. 25, 1972 to F. J. Germino et al.) and U.S. Pat. No.
4,579,944 (issued Apr. 1, 1986 to R. G. Harvey et al.) describe paste
reaction processes for making starch derivatives.
EXAMPLE VI
This example shows that other granular high amylose corn starches can be
jet-cooked and spray-dried using the coupled process. The processing
conditions used for fractionated Potato amylose (about 100% amylose),
unmodified high amylose corn starch (about 50% amylose), and converted
high amylose corn starch (about 70% amylose and having a calcium chloride
viscosity of 25 seconds) are shown in Table II.
The results show that the non-granular powders are highly soluble in cold
water (86.6, 95.3, and 93.0%, respectively) as well as in hot water (99.2,
96.9, and 97.1%). They form strong gels (395, 125 and 104 g/cm.sup.2,
respectively).
EXAMPLE VII
This example demonstrates the use of the coupled jet-cooking/ spray-drying
process to prepare a cold-water-soluble form of a cold-water insensitive
synthetic polymer.
A medium molecular weight fully hydrolyzed polyvinyl alcohol (available
from E. I. DuPont de Nemours under the trade name Elvanol 71-30) was
slurried in water at 3% solids and jet-cooked at 143.degree. C.
(290.degree. F.). Back pressure at the cooking chamber was 55 psig. The
dispersed polymer was conveyed under pressure (45 psig) through an
atomization nozzle (Model 1/2 J82 available from Spraying Systems Inc.)
top mounted in a Niro Utility #1 spray-dryer and atomized with steam at 30
psig. Heated air at 280.degree. C. (536.degree. F.) was used to dry the
atomized solution to a free flowing powder.
The resulting product consisted of rugose spheres generally from 3 to 6
microns in diameter. A total of 31.88% of this material was soluble in
water at 25.degree. C. (77.degree. F.) compared to 3.6% of the unprocessed
polymer. The solubility test used is the one described in U.S. Pat. No.
4,072,535 (issued Feb. 7, 1987 to R. W. Short et al.). DuPont's technical
service bulletin issued December 1965 describes the PVA polymer as having
"excellent resistance to cold water" and requiring elevation to
90.degree.-95.degree. C. (194.degree.-203.degree. F.) for complete
dissolution in water. The viscosity of the spray-dried polymer at
25.degree. C. (77.degree. F.), dispersed in hot water at 4% solids, was 24
cps. compared to 26 cps. for the unprocessed polymer. This shows that the
polymer was not substantially degraded during the processing.
EXAMPLE VIII
This example illustrates the use of the coupled jet-cooking/spray-drying
process to produce a cold-water-soluble powder from a polygalactomannan
gum which is normally difficult to solubilize.
Locust bean gum (available from National Starch Chemical Corp.) was
slurried in water at 1% solids and jet-cooked at 132.degree. C.
(270.degree. F.). Back pressure at the cooking chamber was 30 psig. The
dispersed gum was conveyed under pressure (25 psig) through an atomization
nozzle (Model 1/2 J82) top mounted in a Niro Utility #1 spray-dryer and
atomized with steam at 30 psig. Heated air at 280.degree. C. (536.degree.
F.) was used to dry the atomized mist to a free flowing powder.
The resulting product consisted of rugose spheres generally from 2 to 4
microns in diameter. A total of 71.5% of this powdered gum was soluble in
water at 25.degree. C. (77.degree. F.) compared to 27.1% of the
unprocessed gum. When redispersed in cold water at 4% solids, the
viscosity was 490 cps. within 2 minutes compared to 16 cps. for the
unprocessed gum. The solubility test referred to in Example VII was used.
EXAMPLE IX
This example describes the processing conditions used in the continuous
coupled jet-cooking/spray-drying process when starches other than high
amylose starches are pregelatinized. The equipment used is described in
Example I. The processing variables and results are shown in Table III.
The results show that the non-granular corn, waxy maize, and tapioca starch
powders were essentially 100% cold-water-soluble.
EXAMPLE X
This example compares the flow viscosity of jet-cooked high amylose corn
starch (about 70% amylose) to water at elevated temperatures. High amylose
starch slurries were cooked at solids of about 16.8-18.1%, cooking
temperature of about 149.degree. C. (300.degree. F.), steam flow rate of
168 g./min., and cooking rate of 59.3 ml./min. The resulting flow rates
through the viscometer previously described were 48, 91 and 113 ml./min.
at 20, 40 and 60 psig of pressure using a 0.016 in. orifice in the
atomizer nozzle. For a 0.031 in. orifice, the resulting flow rates were
313-498 and 399-642 ml./min. at 40 and 60 psig. Flow rates of water, under
identical conditions were 100, 138, 190, 600 and 699 ml./min.,
respectively.
It can be seen that jet-cooks of high amylose corn starch flow through the
spray-drying nozzles at rates no less than half that of water when the
temperatures were maintained at from 126.degree. to 153.degree. C.
(259.degree. to 307.degree. F.) even at 28% cook solids. This translates
into a flow viscosity of less than 1 centipoise.
In contrast, when the temperature drops after a 28% solids jet-cook of high
amylose corn starch exits the jet-cooker, the viscosity cannot even be
measured as the starch cook forms a gel in a few seconds.
EXAMPLE XI
This example compares starches pregelatinized using the continuous coupled,
jet-cooking/spray-drying process with the same starches pregelatinized
using the Winkler process (U.S. Pat. No. 3,630,775).
The procedure of the Winkler patent could not be exactly duplicated. The
spraying pressures disclosed in the patent range from 2000 to 6800 psig
and the cooking temperatures range from 182-304.degree. C.
(360.degree.-580.degree. F.). The equipment used for this experiment was
limited to a pressure of 1600 psig and a temperature of 160.degree. C.
(320.degree. F.).
A B.I.F. (a division of New York Air Brake, Providence, R.I.) model 1180
jacketed micro-feeder piston pump was modified to produce higher flow
rates so that pressures up to 1600 psig could be achieved. Thermocouples
were attached to the cooking chamber to monitor the temperature of the
cook. The Piston cavity was filled with starch slurries at 10% to 20%
solids. The slurries were heated for 20 minutes to a temperature of
160.degree. C. (320.degree. F.) with 100 psig of steam flowing through the
jacket of the pump. The starch was then pumped through a single fluid
nozzle having a 0.0135 in. orifice (#80A available from Spraying Systems
Inc.) at 1600 psig pressure. Samples were collected and analyzed for
viscosity or gel strength.
Part A--High Amylose Starch (70% amylose)
Comparative starch samples were sprayed at 1600 psig and 160.degree. C.
(320.degree. F.), collected, and allowed to cool and set-up for 24 hrs. at
21.degree. C. (72.degree. F.).
Gel strengths were run on the Texture Analyzer. Cook solids were run (using
an infra-red heat lamp balance) after the gel strengths were tested.
The jet-cooking conditions used to prepare the pregelatinized starch by the
coupled process were as follows: 28% cook solids (38% slurry solids),
steam flow of 31 g./min., cooking temperature of 143.degree. C.
(290.degree. F.), flow rate of 38.7 ml./min., and back pressure of 52 psig
at the chamber and 48 psig at the nozzle. The spray-dryer used was an
Anhydro Dryer Model No. 1 equipped with a two fluid nozzle (set-up #22B).
The inlet temperature of the spray-dryer was 230.degree. C. (446.degree.
F.) the outlet temperature was 84.degree. C. (183.degree. F.) and air at
20 psig was used for atomization.
The starches were dispersed in hot water and heated in a boiling water bath
for 15 minutes, allowed to cool and set-up for 24 hours at 21.degree. C.
(72.degree. F.). The solids and gel strengths are shown below. The starch
degradation is shown in FIG. 3.
______________________________________
Solids Gel Strength
Sample (%) (g./cm..sup.2)
______________________________________
Indirect cooking/spraying
11.1 370
(comparative) 13.4 580
Continuous coupled
10.3 557
jet-cooking/spray-drying
13.4 768
process 13.8 946
16.6 +996*
______________________________________
*Gel strengths over 950 g are not accurate, as they are over the upper
limits of the Texture Analyzer.
The results show that the high amylose starches prepared by indirect
heating and pressure atomization gave lower gel strengths than the same
starch cooked and atomized by the coupled process using direct heating.
This is attributed to the less effective dispersion formed during indirect
heating and the higher shear developed during atomization in the pressure
nozzle. It would be expected that pressures and temperatures exceeding
those used here, as taught in Winkler, will only further degrade the
starch.
Part B--Other Starches
Comparative starch samples of waxy maize starch (about 0% amylose) and corn
starch (about 28% amylose) were sprayed at 1600 psig at a temperature of
160.degree. C. (320.degree. F.) and allowed to cool to 71.degree. C.
(160.degree. F.) before viscosity measurements were taken.
Waxy maize and corn starch samples pregelatinized using the coupled process
were spray-dried at inlet temperatures of 200.degree. C. (392.degree. F.)
and 200.degree. C. (392.degree. F.), and outlet temperatures of
125.degree. C. (257.degree. F.) and 82.degree. C. (180.degree. F.), using
30 psig of atomization steam and 30 psig of atomization air respectively.
The spray-dryer used for the waxy maize starch was a Niro Utility #1 dryer
equipped with a two fluid nozzle (set-up 22B nozzle and 120 cap). That
used for the corn starch was an Anhydro Model No. 1 dryer with the same
nozzle and set-up.
The recovered starches were dispersed in hot water and heated in a boiling
water bath for 30 minutes and allowed to cool to 71.degree. C.
(160.degree. F.) before viscosity measurements were taken. Cook solids
were run (using an infra-red heat lamp balance) after all samples had been
tested. The solids and viscosities are shown below. The gel strengths are
given in Part A.
______________________________________
Solids Viscosity
Sample (%) (cps)
______________________________________
Waxy Maize prepared by
11.9 423
continuous coupled 15.6 740
jet-cooking/spray- 20.0 1850
drying process
Waxy Maize 10.0 30
prepared by indirect
14.0 37
cooking/spraying 19.4 190
(comparative) 21.2 340
Corn prepared by 12.0 620
continuous coupled 16.3 3650
jet-cooking/spray- 20.4 24500
drying process
Corn prepared by 12.0 28
indirect cooking/ 14.0 37
spraying (comparative)
19.4 190
______________________________________
The results again show that high molecular weight starches, such as native
waxy maize and corn starch, were degraded, as shown by the extreme
reduction in viscosity, when processed using indirect heating and a
pressure nozzle. The starch degradation is shown in FIGS. 4 and 5.
EXAMPLE XII
This example demonstrates that the pregelatinized, spray-dried,
non-granular, amorphous high amylose starches prepared by the coupled
process are unique. X-ray crystallographic scans (see FIG. 2) performed by
Rigaku USA Danvers Mass Model No. DMAX-8 showed that the pregelatinized
high amylose starch (about 70% amylose) prepared by the coupled
jet-cooking/spray-drying process was amorphous, i.e., there were no
crystalline peaks. Comparative pregelatinized starches (about 70% amylose)
prepared by jet-cooking followed by drying on a heated plate unexpectedly
contained crystalline regions. Samples made by jet-cooking followed by
air-drying contained crystalline regions as expected. Native granular
starch likewise contains crystalline regions.
The lack of retrogradation in the coupled jet-cooked/spray-dried material
is confirmed by the higher gel strength on redispersion (160 g./cm..sup.2
at 6% solids in hot water). The same high amylose starch Processed by
jet-cooking and drum-drying had a gel strength of only 110 g./cm..sup.2 on
redispersion.
It is well known that retrograded starches do not provide as strong a gel
on redispersion below 100.degree. C. (212.degree. F.) compared to a more
soluble starch of equal amylose content. This is due to the unavailability
of the retrograded amylose for gel formation.
EXAMPLE XIII
Scanning Electron Microscope photomicrographs of pregelatinized high
amylose (about 70% amylose) corn starches prepared by the present coupled
jet-cooking/spray-drying process (Photograph A), the simultaneous
atomization and cooking process of U.S. Pat. No. 4,280,851 (Photograph B),
and the autoclaving/drum-drying process of U.S. Pat. No. 3,086,890
(Photograph C) are shown in FIG. 6. The photomicrographs of the particles
that make up the powders of these starches show distinct physical
differences.
The powders of the current invention are composed of non-granular, round,
spray-dried particles having convoluted (dimpled) surfaces due to the
rapid removal of water and subsequent collapse of the starch-film during
drying. In this process, the size of the particles are determined by the
size of the droplets formed during atomization and drying. These particles
are unlike those prepared by the simultaneous atomization and cooking
process which are generally in the form of swollen granules. This is
evidenced by the slightly wrinkled surfaces characteristic of intact,
swollen starch granules. Though a spray-dried Particle, the starch in this
photomicrograph (photograph B) was never placed into solution and the
particle size is determined largely by the degree of granular swelling
during cooking. The powders of the autoclaving/drum-drying process are in
the form of angular flakes. The particle size is determined by subsequent
grinding and fractionation of the drum-dried sheet after drying.
The preparation of a spray-dried high amylose starch by the process of the
Pitchon patent (U.S. Pat. No. 4,250,851) was difficult, and the resulting
product was considerably less soluble and contained intact, non-degraded
granules. As previously shown, the preparation of such a starch by the
coupled process was easily carried out.
EXAMPLE XIV
This example compares the displacement density and bulk density of various
pregelatinized starches prepared by the present coupled
jet-cooking/spray-drying process at high solids, a conventional
spray-drying process at low solids, and the jet-cooking/drum-drying
process similar to that of Sarko (U.S. Pat. No. 3,086,890) at low solids.
The starches prepared by the coupled process were prepared using suitable
processing conditions for the particular starch source.
The results in FIG. 7 show that the relationship between displacement
density and bulk density for the various methods of preparing
pregelatinized starches are specific and generally lie within regions that
are independent of the starch source. These density differences are due to
the differences in particle shape and structure resulting from the drying
step of each process.
Particles produced by the Sarko process are flakes which contain less
included air than starch powders spray-dried from dispersions; thus, the
density of the individual Sarko process particle (i.e., displacement
density) is higher than that of spray-dried starch powders from
dispersions. However, these angular flakes pack together less efficiently
than spheres giving a lower bulk density.
Spray-dried starch particles dried from a dispersion generally are
characterized by internal air voids and surface ridges and depressions.
This structure is formed, in the spray-dryer, as the wet atomized
dispersion droplet forms an air and water vapor filled bubble on heating
and collapses on drying. Displacement density is strongly affected by the
amount of included air which is influenced by starch type, dispersion
solids, atomization variables, and spray-dryer conditions. Packed bulk
density varies with particle size distribution in the powder and
smoothness of the particle surface (depth of surface depressions). The
coupled jet-cooking/spray-drying process yields starch powders with higher
bulk densities than conventional spray-drying when using the same high
viscosity base starch.
These physical differences can be used to identify the process by which the
starches were prepared when supplemented with the differences in physical
structure already discussed in previous Examples. The only exception in
the data is the isolated potato amylose prepared by the coupled process,
which lies in region I.
______________________________________
Summary of FIG. 7
Displacement
Bulk
Density Density
Process Region (g/cc) (lbs/ft.sup.3)
______________________________________
Conventional jet-
I low low
cooking/spray-drying
Coupled jet- II low high
cooking/spray-drying
Jet-cooking/ III high low-high
drum-drying
______________________________________
Now that the preferred embodiments of the invention have been described in
detail, various modifications and improvements thereon will become readily
apparent to those skilled in the art. Accordingly, the spirit and scope of
the present invention are to be limited only by the appended claims and
not by the foregoing specification.
TABLE I
__________________________________________________________________________
Process Conditions for Jet-Cooking/Spray-Drying
High Amylose Starch (70% amylose)
(1) (2) (3) (4) (5)
__________________________________________________________________________
Slurry Solids 21.0
21.5 22.0 22.5 42.5
Cook Solids 13.0 13.0 13.0 13.0 28.0
Jet Cooking Temperature
143 (290)
143 (290)
143 (290)
143 (290)
143 (290)
Steam Flow (g./min.)
20.0 24.0 36.0 62.0 9.25 lb./min.
Cook Flow (ml./min.)
30.0 30.0 30.0 30.0 3.8 gal./min.
Nozzle Type
Nozzle Set-up 22 22 B 22 B 22 B 1J-152
Dryer Inlet Temp .degree.C.(.degree.F.)
220 (428)
220 (428)
220 (428)
220 (428)
239-191
(446-375)
Dryer Outlet Temp .degree.C.(.degree.F.)
82 (180)
82 (180)
82 (180)
82 (180)
82-96
(180-205)
Atomizer Air (psig)
20.0 20.0 20.0 20.0 120.0 (steam)
Gel Strength (g./cm..sup.2)
194.0
215.0
204.0
134.0
200.1
__________________________________________________________________________
TABLE II
__________________________________________________________________________
Process Conditions for Jet-Cooking/Spray Drying
Various High Amylose Corn Starch
Fractionated Fluidity High Amylose Corn
Potato Amylose
High Amylose Corn
(about 70% amylose; about
(about 100% amylose)
(about 50% Amylose)
25 CaCl.sub.2 viscosity)
__________________________________________________________________________
Slurry Solids 20.0 26.7 30.0
Cook Solids 12.5 16.0 21.0
Jet Cooking Temperature .degree.C.(.degree.F.)
154 (310) 143 (290) 143 (290)
Steam Flow (g./min.)
27.5 27.5 27.5
Cook Flow (ml./min.)
19.9 27.0 39.7
Nozzle Type 2 FLUID 2 FLUID 2 FLUID
Nozzle Set-Up 22 B 22 22
Dryer Inlet Temperature .degree.C.(.degree.F.)
225 (437) 230 (446) 220 (428)
Dryer Outlet Temperature .degree.C.(.degree.F.)
86 (187) 85 (185) 88 (190)
Atomizer Air (psig)
40.0 20 20.0
Cold Water Solubility (%)
86.6 95.3 93.0
Hot Water Solubility (%)
99.2 96.9 97.1
Gel Strength (g./cm..sup.2)
395 125 104
__________________________________________________________________________
TABLE III
__________________________________________________________________________
Process Conditions for Jet-Cooking/Spray-Drying
Other Starches
Corn Starch
Waxy Maize Starch
Tapioca Starch
__________________________________________________________________________
Slurry Solids 20.0 20.0 20.0
Cook Solids 14.0 14.2 11.0
Jet Cook Temperature .degree.C.(.degree.F.)
143 (289)
152 (305) 160 (320)
Steam Flow (g/min)
35.0 31.0 47.0
Cook Flow (ml/min)
20.5-28.8
18.9-21.2 11.3-16.9
Nozzle Type 2 FLUID
2 FLUID 2 FLUID
Nozzle Set-Up 22 B 22 B 22 B
Dryer Inlet Temp .degree.C.(.degree.F.)
225 (437)
225 (437) 218 (424)
Dryer Outlet Temp .degree.C.(.degree.F.)
86 (187)
97 (207) 95.0 (203)
Atomizing Air PSI
20-25 25.5 15.0
Moisture (%) 5.0 5.6 5.0
1% Solids pH 6.5 6.8 6.9
Cold Water Solubility (%)
98.6 97.7 100.0
__________________________________________________________________________
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